1. Field of the Invention
The present invention relates to a gas turbine combustor and, more particularly, to a structure of a gas turbine combustor.
2. Description of the Related Art
FIGS. 16A and 16B show a conventional gas turbine combustor. FIG. 16A is a diagram showing the layout of the combustor within an intake chamber. A plurality of gas turbine combustors 10 are laid out in an approximately ring-shaped intake chamber 30 that is formed with a casing 20 consisting of an external casing 21 and an internal casing 22 (only one gas turbine combustor is shown in the drawing).
Air from a compressor enters the intake chamber 30, and passes through the surrounding of the combustor 10 and enters the inside of the combustor 10 from an air inlet opening 11 at an upper portion of the combustor. The air is pre-mixed with a fuel separately introduced from a fuel nozzle 40. The mixture is combusted within the combustor 10, and the combustion gas is supplied to a turbine.
FIG. 16B is a cross-sectional diagram of an enlarged portion of (B) in FIG. 16A. A wall 100 of the combustor 10 is constructed of a first wall 200 that extends straight at the fuel nozzle 40 side, and a second wall 200′ that is inclined at a turbine chamber side. The first wall 200 is a cooling wall provided with a clearance through which cooling air passes. The second wall 200′ is a double wall cooled with vapor. Both walls are connected to each other via a spring clip 105.
FIGS. 17A and 17B show a state where a combustor 10 is supplied with a cover 50 to form a convection cooling path 60, based on the structure shown in FIGS. 16A and 16B respectively. The air from the compressor is guided to the convection cooling path 60 to cool the combustor 10, and is then guided to the inside of the combustor 10. A first wall 200 and a second wall 200′ of the combustor 10 have the same structures as those shown in FIG. 16B respectively. The first wall 200 and the second wall 200′ shown in FIG. 16B and FIG. 17B respectively are acoustically very rigid boundaries, and they hardly transmit sound waves. Therefore, the resonance magnification of a sound field within the combustor 10 becomes high, and this can easily bring about what is called a combustion oscillation phenomenon.
The combustion oscillation is a phenomenon that a frequency component of a pressure variation of a combustion gas generated due to a generation of a combustion variation relative to a natural frequency of the sound field is amplified, and the pressure variation within the combustor 10 becomes larger. As a result, the quantities of the fuel and air introduced respectively into the combustor 10 vary, which makes the combustion variation much larger.
Particularly, a high-frequency combustion oscillation corresponding to an acoustic mode generated with a cross section of the combustor 10 is strongly influenced by the acoustic characteristics of the wall 100 of the combustor 10. This combustion oscillation occurs very easily when the wall 100 of the combustor 10 is acoustically rigid.
In recent years, along a inforcement of exhaust gas emission controls and, particularly, the inforcement of the Nox restrictions, it has become necessary to increase the ratio of the quantity of air to the quantity of fuel. In other words, it has become necessary to implement lean combustion based on a large air-to-fuel ratio. When the lean combustion is implemented, a combustion variation can occur very easily. This easily brings about a variation in the pressure of the combustion gas. Therefore, it has been strongly demanded to provide a combustor that can prevent the amplification of the pressure variation of the combustion gas in the sound field, and can restrict the occurrence of the combustion oscillation.